Integrated circuits (ICs) are generally formed in a “package” that has electrical connections (e.g. leads, pins, balls, etc.) between an IC die inside the package and the outside of the package. The IC die must be protected to prevent damage to it, so the IC die is commonly surrounded by a material that is highly impervious to air, moisture, shock and other potentially hazardous environmental conditions. The protective material is also commonly a poor thermal conductor, so to improve heat dissipation from the IC die, a heat spreader (commonly called a “drop-in heat spreader”) is included in the IC package to transfer heat from the IC die to the surrounding environment. The heat spreader may also be used to attenuate EMI emissions from the IC package.
A prior art heat spreader 100 is shown in FIGS. 1 and 2. In FIG. 2, the heat spreader 100 is shown in cross section (at section 2-2 in FIG. 1) as part of an IC package 102. The IC package 102 also includes an IC die 104, a substrate 106, several wire bonds 108, a molding compound 110 and several solder balls 112 (e.g. for a ball grid array, “BGA”). The heat spreader 100 is mounted on the substrate 106 to cover the IC die 104 and the wire bonds 108. (Other heat spreader technology places the drop-in heat spreader under the die, so the wire bond loops don't affect the placement.) The heat spreader 100 has a raised circular portion 114 that surrounds the IC die 104 and the wire bonds 108. The heat spreader 100 also has dimples 116 that are electrically connected to the substrate 106 to ground the heat spreader 100 for EMI attenuation purposes.
Heat from the IC die 104 generally radiates through the molding compound 110 to the heat spreader 100 as well as through the substrate 106. From the heat spreader 100 and the substrate 106 the heat is dissipated to the environment. It is preferable that most of the heat dissipates through the heat spreader 100, because the substrate 106 may have components, such as the solder balls 112, that are vulnerable to heat.
The amount of heat that can be dissipated by the heat spreader 100, instead of through any other part of the IC package 102, largely depends on the thermal conductive properties of the molding compound 110 (e.g. a higher thermal conductivity is better for this consideration) and the distance between the heat spreader 100 and the source of the heat, i.e. the IC die 104 (e.g. a closer distance is better for this consideration). The molding compound 110, however, is selected not for its thermal conductive properties, but rather for a variety of other important characteristics. As a result, the molding compound 110 commonly has poor thermal conductive properties. Additionally, the distance between the heat spreader 100 and the IC die 104 is limited by clearance requirements for the loops of the wire bonds 108.
The problem of the distance between the heat spreader 100 and the IC die 104 is further exacerbated by a continuing trend in IC packaging technologies to increase the number and/or density of the BGA solder balls 112. The prior art example shown in FIG. 2 includes three rows of I/O (input/output) pads 118 along each edge of the IC die 104. However, IC dies having four or five, or more, rows are being developed. The wire bonds 108 that connect to the inner rows of I/O pads 118 have to extend with sufficient clearance over the wire bonds 108 that connect to the outer rows of I/O pads 118. Therefore, if an IC die has more rows of I/O pads 118, the wire bonds 108 for the innermost row will have to extend higher to properly pass over the wire bonds 108 of the other rows. In order to accommodate the higher wire bonds 108, however, the distance between the heat spreader 100 and the IC die 104 will have to be increased. The increased distance between the heat spreader 100 and the IC die 104 will decrease the efficiency with which the heat spreader 100 can dissipate the heat from the IC die 104. Additionally, costly new manufacturing tools will have to be developed to handle the IC packages 102 having a greater height dimension.
It is with respect to these and other considerations that the present invention has evolved.